Towertalk
[Top] [All Lists]

[TowerTalk] High Antenna Modelling

To: <towertalk@contesting.com>
Subject: [TowerTalk] High Antenna Modelling
From: n4zr@contesting.com (Pete Smith)
Date: Sat, 02 Feb 2002 10:45:54 -0500
At 09:12 AM 2/2/02 -0600, n4kg@juno.com wrote:
...
>At 6 wavelengths above ground, the peaks and nulls alternate 
>every 2.5 degrees over perfectly flat ground.  In real life, small
>changes in slope can cause the nulls to 'fill in', if not completely,
>at least enough to become harder to detect when the peaks 
>and nulls are close together, i.e., when the antennas are more
>than 4 wavelengths high (> 140 ft on 10M, 190 ft on 15M, etc).

As Tom's explanation of null formation suggests, some foreground slope
angles and distances from the antenna may actually deepen a given null or
nulls.

I think there is probably another phenomenon at work with very high
antennas, and that is a "smearing" of the arrival angle of signals due to
ionospheric irregularities.  We talk about a signal arriving at 8 degrees,
for example, but the physical reality may be that its energy is spread over
7-9 degrees instead.  With a very high antenna with closely spaced lobes
and nulls, all of the energy of an arriving signal is unlikely to fall only
in as null.  This could explain the perception that the nulls have
disappeared.     

73, Pete N4ZR

Sometimes a tower is
just a tower





________________________________________________________________________
Where do you get ICE bandpass filters & beverage matching boxes?  The
same place that pays for the hosting of this list:  The eHam Store.
Order online at http://store.eham.net.
-----------------------------------------------------------------------

-----
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com


<Prev in Thread] Current Thread [Next in Thread>